1. Field of the Invention
The present invention relates to an antenna device using a dielectric antenna.
2. Description of the Related Art
Conventionally, in communication equipment, a surface mounting antenna using a dielectric, i.e., a dielectric antenna has been used as one of antenna elements mounted onto a wireless circuit substrate. In the dielectric antenna, a radiation electrode for antenna operation is provided on a dielectric substrate. Conventionally, an open-end type antenna such as a monopole antenna or an inverse F-type antenna using this dielectric antenna has been a mainstream.
In general, in the case of an open-end type antenna such as a monopole antenna or an inverse F-type antenna, impedance of the open end is high, and thus, the distance between a mounted antenna element and a ground needs to be ensured as long as possible. For this purpose, in order to sufficiently ensure antenna performance, the antenna element needs to be far away from a ground plane by removing the ground around the periphery of the mounted antenna element in a substrate on which a ground plane is formed. However, when a dielectric antenna is actually mounted as an antenna element onto a substrate, a space (antenna-occupied area) which can be used as an antenna is often limited by taking into consideration size reduction of equipment. Consequently, sufficient antenna performance cannot be exhibited by the influence of the ground around the periphery of the antenna element. Hence, the position where an antenna element is mounted is often set at the end of a substrate in order to minimize the influence of the ground.
In the conventional technique, for example, Patent Document 1 discloses an antenna structure in which a capacitance power supply radiation electrode for antenna operation is provided on a base member, the base member is mounted on a non-ground area of a circuit substrate, and a grounding line for electrically connecting an earth electrode on the circuit substrate and the radiation electrode on the base member is provided. In the antenna structure, the grounding line has a shape having a folded back portion. In addition, Patent Document 2 discloses an antenna structure that comprises a surface mounting antenna in which a radiation electrode for antenna operation is formed on a base member and a substrate having a ground area where a ground electrode is formed and a non-ground area where no ground electrode is formed, wherein the one end side of the radiation electrode is a ground connection portion which is grounded to the ground electrode.